It is common to use tubular apparatus in fluid handling systems. In many such systems, the tubular apparatus is subjected to wear, abrasion and corrosion primarily due to the abrasiveness of the material transported, the ambient temperature and chemical degradation. In severe uses, such as in the process of pumping oil from oil wells, the interior surfaces of the tubing and other components are exposed to highly abrasive and corrosive elements, such as hydrogen sulfide and sulfuric acid, for example. The pumping of oil creates an environment laden with corrosive and abrasive matter, often at both high and low temperatures.
There is disclosed in the prior art methods of providing a resistant coating or layer on a metal surface so as to increase the wear, abrasion and corrosion resistivity of the surface. For example, it is known from U.S. Pat. No. 2,801,187 (Galmiche et al.) that a resistant metal layer can be created on surfaces by chemical vapour deposition of the metal. In that patent, the method disclosed requires two distinct halide sources and the pack compositions used create layers that include any of the following metals: chromium, aluminium, nickel and molybdenum.
In U.S. Pat. No. 3,842,921 (Dill et al.) a method for making a wear-resistant boron drill is disclosed. The method includes carburizing a metal surface with a layer containing significant amounts of carbon, and then boronizing the carburized layer. The resultant product is then hardened and tempered. U.S. Pat. No. 3,923,348 (Peck) also discloses a method in which a carburized layer is formed, followed by a boronized layer. Both of these patents relate to the treatment of outside surfaces of metal parts.
U.S. Pat. No. 4,495,005 (Aves, Jr.) discloses a method for carburizing and borosiliconizing a metal surface. The method includes the step of exposing the metal surface to diffusible carbon, boron and silicon found in a single pack composition at different stages during a single thermocycle. The temperature is controlled so that in the initial stage only carburizing of the metal surface occurs, whereas in the subsequent stages, boronizing and siliconizing occur. As such, two or more distinct layers are formed on the metal surface. The method disclosed in U.S. Pat. No. 4,495,005 is directed to the treatment of outside surfaces. The method is not useful for treating tube interior surfaces, because the pack tends to adhere during the chemical vapor deposition process because the barium and calcium oxides present in the pack adhere to form a cohesive pack which is no longer free flowing.
U.S. Pat. No. 4,389,439 (Clark et al.) discloses a method for treating the inner surface of a pipe by forming a dual layer on the inner surface. The first layer consists mostly of iron carbide formed by carburizing or carbonitriding. This is done by contacting the inner surface of the tubes with a carbon source for five hours at 1625.degree. F. The inside surface of the tubing is then exposed to a boronizing pack comprising 2% -10% boron powder, a halogen activator and aluminum oxide filler. This pack is heated for 8 hours at 1650.degree. F., however, since this pack contains a major portion of aluminum oxide, the pack will sinter, or least the pack will adhere to itself and/or adhere to the inner surface of the tube. Thus, after treatment of the inside surface is completed, the adhered pack can only be removed from the tube interior by breaking up the adhered pack. As such, only localized areas of the tube interior can be treated at one time, rather than treating the entire length of a long tube.
A chemical vapour deposition method has been provided in the prior art for treating an interior surface of a ferrous tubular member to provide abrasion and corrosion resistance to the surface. In the process of the prior art, the surface to be treated is exposed to a pack composition, and both are heated to a temperature where at least one carburized, boronized or siliconized layer is formed on the surface by chemical vapour deposition. Preferably, a first carburized or carbonitride layer is formed, followed by a boronized and/or siliconized layer.
In this specification, the term "adheres" is used to refer to the condition where the pack composition either sinters, or it adheres to itself and/or adheres to the tubular member's surface. Thus, in order for the adhered pack composition to be removed from the tubular member, it must be broken up since the pack composition is not free-flowing. Therefore, by "adhered pack composition", it is meant that the pack composition no longer is free-flowing and that it must be broken up before it can be removed from the interior of the tubular member. In addition, tubular member is intended to include any tubular elongate hollow member of extended length, normally longer than 4 feet.
Accordingly, it would be advantageous to provide a method for treating the entire length of an inner surface of a long tubular member.